Field of the Invention
The present invention relates to a mirror drive device equipped with a mechanism for high-speed driving of a mirror unit provided in an image pickup apparatus, such as a single-lens reflex camera, and an image pickup apparatus equipped with the mirror drive device.
Description of the Related Art
In a quick return mirror mechanism e.g. of a single-lens reflex camera, a mirror unit provided with a main mirror and a sub mirror is moved at high speed between a mirror-down position in which the mirror unit enters a photographing optical path and a mirror-up position in which the mirror unit is retracted from the photographing optical path. Each of the mirrors of the mirror unit is brought into contact with a stopper formed in a mirror box, at the mirror-down position, thereby being held in a predetermined stop position, to guide an object light flux having passed through a photographic optical system of the lens unit to a viewfinder optical system and a focus detection unit.
Conventionally, there has been proposed a mirror drive device that drives the mirror unit between the mirror-down position and the mirror-up position by transmitting a driving force to the main mirror of the mirror unit and causing the sub mirror to follow the main mirror using a toggle spring and a reversing cam. In the proposed mirror drive device, the toggle spring urges the sub mirror in a mirror-down direction when the mirror unit is in the mirror-down position, and urges the same in a mirror-up direction when the mirror unit is in the mirror-up position (see Japanese Patent Laid-Open Publication No. 2011-85762).
According to the mirror drive device proposed in Japanese Patent Laid-Open Publication No. 2011-85762, in order to achieve high turning speed of the mirror unit, it is required to increase the spring force of the toggle spring for urging the sub mirror. However, if the spring force of the toggle spring is increased, the mirror unit reaches the mirror-down position or the mirror-up position at the increased turning speed of the sub mirror and the main mirror, which causes a large bounce of each mirror and an increase in mirror driving sound.
Further, according to the mirror drive device proposed in Japanese Patent Laid-Open Publication No. 2011-85762, a large torque is required for reversing the urging direction of the toggle spring for urging the sub mirror following the main mirror between the mirror-up position and the mirror-down position. For this reason, there is a limit to increasing mirror driving speed. Further, a large load is applied to the reversing cam that reverses the direction of urging the sub mirror, and hence there is concern about the durability of the mirror drive device.